Carbon dioxide fixation by epidermal and mesophyll tissues of Tulipa and Commelina

Rates of (14)CO2 fixation by epidermal tissue of Tulipa gesneriana (tulip) and Commelina diffusa are only slightly higher in the light than in the dark while in mesophyl tissues rates are much greater in the light. The first products of (14)CO2 fixation by epidermal tissue of Tulipa gesneriana and C. diffusa in the light and dark are malate and aspartate. In addition to these dominating dicarboxylic acids, 3-phosphoglyceric acid and sugar phosphates appear in the light, while in the dark only the amino acids, glutamate and glutamine become labelled. Mesophyll tissue of tulip and C. diffusa, however, gives typical CO2 fixation patterns of the labelled products of C3 plants. Furthermore, a period of dark (14)CO2 fixation followed by a light (12)CO2 chase carried out with epidermal tissue suggested that malate can act has the precursor of phosphorylated compounds of the Calvin cycle and consequently of starch. The data are consistent with the view that guard cells are able to exhibit Crassulacean acid metabolism.